Long Term Evolution (LTE) supports data rates up to 100 Mbps in the downlink and 50 Mbps in the uplink. LTE-Advanced (LTE-A) provides a fivefold improvement in downlink data rates relative to LTE using, among other techniques, carrier aggregation. Carrier aggregation may support, for example, flexible bandwidth assignments up to 100 MHz. Carriers are known as component carriers in LTE-A.
LTE-A may operate in symmetric and asymmetric configurations with respect to component carrier size and the number of component carriers. This is supported through the use or aggregation of up to five 20 MHz component carriers. For example, a single contiguous downlink (DL) 40 MHz LTE-A aggregation of multiple component carriers may be paired with a single 15 MHz uplink (UL) carrier. Non-contiguous LTE-A DL aggregate carrier assignments may therefore not correspond with the UL aggregate carrier assignment.
Aggregate carrier bandwidth may be contiguous where multiple adjacent component carriers may occupy continuous 10, 40 or 60 MHz. Aggregate carrier bandwidth may also be non-contiguous where one aggregate carrier may be built from more than one, but not necessarily adjacent component carriers. For example, a first DL component carrier of 15 MHz may be aggregated with a second non-adjacent DL component carrier of 10 MHz, yielding an overall 25 MHz aggregate bandwidth for LTE-A. Moreover, component carriers may be situated at varying pairing distances. For example, the 15 and 10 MHz component carriers may be separated by 30 MHz, or in another setting, by only 20 MHz. As such, the number, size and continuity of component carriers may be different in the UL and DL.
In order to access LTE-A for DL and UL transmissions, a wireless transmit/receive unit (WTRU) may need to know DL and UL carrier configurations in terms of bandwidth, DL and UL component carrier pairings, random access parameters, and other LTE-A system specific information. Carrier aggregation information, such as the identity of the carrier, may also need to be conveyed from a base station to the WTRU. Control information with respect to carrier aggregation implementation may be carried over a physical downlink control channel (PDCCH). The requirements for the PDCCH may need to be defined and the WTRU may need to know the time and frequency location of the PDCCH to obtain the control information.